263 research outputs found
Full-gap superconductivity robust against disorder in heavy-fermion CeCu2Si2
A key aspect of unconventional pairing by the antiferromagnetic
spin-fluctuation mechanism is that the superconducting energy gap must have
opposite sign on different parts of the Fermi surface. Recent observations of
non-nodal gap structure in the heavy-fermion superconductor CeCuSi were
then very surprising, given that this material has long been considered a
prototypical example of a superconductor where the Cooper pairing is
magnetically mediated. Here we present a study of the effect of controlled
point defects, introduced by electron irradiation, on the temperature-dependent
magnetic penetration depth in CeCuSi. We find that the
fully-gapped state is robust against disorder, demonstrating that low-energy
bound states, expected for sign-changing gap structures, are not induced by
nonmagnetic impurities. This provides bulk evidence for -wave
superconductivity without sign reversal.Comment: 5 pages, 4 figures + Supplemental Material (1 page, 1 figure). Will
appear in Phys. Rev. Let
Correlation between Fermi surface transformations and superconductivity in the electron-doped high- superconductor NdCeCuO
Two critical points have been revealed in the normal-state phase diagram of
the electron-doped cuprate superconductor NdCeCuO by exploring
the Fermi surface properties of high quality single crystals by high-field
magnetotransport. First, the quantitative analysis of the Shubnikov-de Haas
effect shows that the weak superlattice potential responsible for the Fermi
surface reconstruction in the overdoped regime extrapolates to zero at the
doping level corresponding to the onset of superconductivity.
Second, the high-field Hall coefficient exhibits a sharp drop right below
optimal doping where the superconducting transition
temperature is maximum. This drop is most likely caused by the onset of
long-range antiferromagnetic ordering. Thus, the superconducting dome appears
to be pinned by two critical points to the normal state phase diagram.Comment: 9 pages; 7 figures; 1 tabl
Controlling crystal cleavage in Focused Ion Beam shaped specimens for surface spectroscopy
Our understanding of quantum materials is commonly based on precise
determinations of their electronic spectrum by spectroscopic means, most
notably angle-resolved photoemission spectroscopy (ARPES) and scanning
tunneling microscopy (STM). Both require atomically clean and flat crystal
surfaces which traditionally are prepared by in-situ mechanical cleaving in
ultrahigh vacuum chambers. We present a new approach that addresses three main
issues of the current state-of-the-art methods: 1) Cleaving is a highly
stochastic and thus inefficient process; 2) Fracture processes are governed by
the bonds in a bulk crystal, and many materials and surfaces simply do not
cleave; 3) The location of the cleave is random, preventing data collection at
specified regions of interest. Our new workflow is based on Focused Ion Beam
(FIB) machining of micro-stress lenses in which shape (rather than crystalline)
anisotropy dictates the plane of cleavage, which can be placed at a specific
target layer. As proof-of-principle we show ARPES results from micro-cleaves of
SrRuO along the ac plane and from two surface orientations of
SrTiO, a notoriously difficult to cleave cubic perovskite
Effect of a dopexamine induced increase in cardiac output on splanchnic hemodynamics in septic shock
Observation of the Non-linear Meissner Effect
A long-standing theoretical prediction is that in clean, nodal unconventional
superconductors the magnetic penetration depth , at zero temperature,
varies linearly with magnetic field. This non-linear Meissner effect is an
equally important manifestation of the nodal state as the well studied
linear-in- dependence of , but has never been convincingly
experimentally observed. Here we present measurements of the nodal
superconductors CeCoIn and LaFePO which clearly show this non-linear
Meissner effect. We further show how the effect of a small dc magnetic field on
can be used to distinguish gap nodes from non-nodal deep gap
minima. Our measurements of KFeAs suggest that this material has such a
non-nodal state
Fermi Surface of the Electron-doped Cuprate Superconductor Nd_{2-x}Ce_xCuO_{4} Probed by High-Field Magnetotransport
We report on the study of the Fermi surface of the electron-doped cuprate
superconductor NdCeCuO by measuring the interlayer
magnetoresistance as a function of the strength and orientation of the applied
magnetic field. We performed experiments in both steady and pulsed magnetic
fields on high-quality single crystals with Ce concentrations of to
0.17. In the overdoped regime of we found both semiclassical
angle-dependent magnetoresistance oscillations (AMRO) and Shubnikov-de Haas
(SdH) oscillations. The combined AMRO and SdH data clearly show that the
appearance of fast SdH oscillations in strongly overdoped samples is caused by
magnetic breakdown. This observation provides clear evidence for a
reconstructed multiply-connected Fermi surface up to the very end of the
overdoped regime at . The strength of the superlattice potential
responsible for the reconstructed Fermi surface is found to decrease with
increasing doping level and likely vanishes at the same carrier concentration
as superconductivity, suggesting a close relation between translational
symmetry breaking and superconducting pairing. A detailed analysis of the
high-resolution SdH data allowed us to determine the effective cyclotron mass
and Dingle temperature, as well as to estimate the magnetic breakdown field in
the overdoped regime.Comment: 23 pages, 8 figure
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